can you microwave cardboard

Can you microwave cardboard? Was your takeout order cold when it arrived? Did you stop in front of the microwave because you were unsure of whether or not you could reheat it in its container? Is the box made of cardboard?

Did you check for a microwave-friendly sign and not spot one? Are you confused and wondering, can you microwave cardboard?

In this article, we will be talking about whether or not it’s safe to use cardboard food containers in microwaves.

Let’s start with some science!

How Do Microwaves Work?

Long wavelength-low frequency electromagnetic waves that fit in the range between infrared radiation and radio waves are called microwaves.

In a microwave, an electron tube called the magnetron produces these microwaves. They are channeled into the appliance’s interior through an antenna.

When you put food in the appliance and turn it on, the microwaves are readily absorbed by water, fat, and sugar molecules in your food.

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These “agitate” your food’s inner particles, causing them to vibrate. The friction generated is then changed to heat energy, which is why your food gets hot.

How Do They Work on Non-Food Items?

microwave non food

The answer to this mystery lies (mostly) in the water molecules found in non-food items.

Plastic, for example, will not get hot as there is no water content in the material. If your plastic dish is hot, it is because you heated your food for too long and the excess heat has transferred to your plastic container. 

Since food heats up quicker on the outside, it is prudent to stop after a few seconds, stir your food and then decide if you need to warm it more.

As earthenware has some water molecules, it tends to feel warm to the touch. Stoneware, however, has no water molecules and will not heat.

Metals reflect microwaves, and in the absence of food or other non-metallic items, these long wavelength-low frequency electromagnetic waves will destroy your appliance.

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Glass will heat, yes. But glass has no water molecules. However, it has impurities that are loosely bound and can move around when stimulated by microwaves.

Now that we know this side of the equation, let’s understand the other.

What is Cardboard?

It is a paper product. It can be made either from wood chips or from partially recycled paper.

In the simplest terms, paper pulp is set in a corrugated shape and glued between two paper sheets.

For food-grade containers, the glue is mostly made from water and starch. This makes it safe as a food packaging material.

Can You Put a Cardboard in the Microwave?

The short answer is yes. Here’s a scientific breakdown for why. The compressing, recycling, and manufacturing processes involve water or water-based glue products.

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This is what makes it safe. However, not all cardboard is manufactured the same way. Some even have added chemicals, wax, metals, and ink.

Hence, you need to figure out what kind you are dealing with before placing it in your appliance.

Cardboard boxes and food containers should come with a microwave-safe icon on them.

If not, there will be some indication letting you know if they are safe to microwave or not. Even then, you still need to follow some precautions.

Can you Microwave Cardboard – What Would Happen?

microwave cardboard

Just like it is safe to put paper plates in the microwave, it is also generally safe to put cardboard.

You can experiment with some, but use one without any print on it. Seeing as the microwave works by charging up water molecules in food and cardboard has some, it should warm up.

Depending on what kind you are using there is a slight possibility of food damage or fires.

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Here are the red flags you need to watch out for:

1. Check the Label

If it’s a takeout container or frozen meal like this one, there’s a good chance the packaging will have a label on it letting you know can you microwave cardboard box or not.

Remember to check the boxes. The icon is usually a small microwave with a green tick symbol on it. If you can’t find such an icon, look at the instructions section.

The instructions will let you know how to heat your food on the stove, in an oven, or microwave. If the container does not have an icon or label, then be safe and do not microwave it.

2. Check for Metal

Some containers might contain small metal traces, usually from transference, which makes them unsafe to microwave. This is rare in food-grade boxes, however.

If you are experimenting with non-food grade containers, double and triple-check for metal.

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Equally, some Chinese restaurants add metal handles to takeout containers. So, if you are not reheating pizza, give the takeout container a once over.

3. Chemicals

Containers with a waxy coating or plastic layer should not be microwaved. The same applies to cardboard containers with Styrofoam or printed ink.

These additional elements can melt and release toxic fumes. Furthermore, the chemicals released could enter your food.

Can you microwave it?


But should you?

Not Always.

4. Microwave Temperature

Nothing wrong with a little precaution. Check your microwave’s temperature settings and set it to low if you are warming food in a cardboard container.

Numerous manufacturers contend it’s safe to microwave cardboard but advise that you lower the strength and not leave the microwave unattended when in use.

5. Type of Food You’re Warming

Do not try to warm food in closed containers in the microwave, especially if liquids. This is because the microwaves generate a lot of heat in food, and it radiates much slower if the box is closed.

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This will cause the pressure in the container to rise as heat tries to escape. The result, explosion accidents. Also, make sure there’s always some food in the container.

Never heat an empty container, especially cardboard. You need food inside the container to absorb the microwaves; otherwise, the box might dry enough to catch fire.

How Long Can You Put Cardboard in the Microwave?

Certainly not for as long as you like—there’s a threshold for how long anything can be heated.

If you are cooking frozen foods, the label will usually indicate how long the container needs to be microwaved as well as the power level.

There are way too many variants in cardboard to arrive at a single standard interval but use your judgment here.

Gauge the strength of your appliance and only warm the container for short durations. If your food hasn’t warmed up enough, you can always wait a few seconds and put it back in for another round.

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Some Final Thoughts

If you don’t have a fire extinguisher, you should also consider buying a small fire extinguisher for your kitchen.

After all, kitchens are where most fires start, and experimenting to figure out can you microwave cardboard without precautions is generally a recipe for disaster.

Also, just a friendly reminder—do not leave your food unattended when it’s in the microwave, especially if it’s in a cardboard box. Burnt cardboard will ruin your food and your day. It’s worth the caution.

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